Minor tweaks (#10987)

### What problem does this PR solve?

1. Rename identifier name
2. Fix some return statement
3. Fix some typos

### Type of change

- [x] Refactoring

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

api/db/services/document_service.py

@@ -985,7 +985,7 @@ def doc_upload_and_parse(conversation_id, file_objs, user_id):
                     "content_with_weight": mind_map,
                     "knowledge_graph_kwd": "mind_map"
                 })
-            except Exception as e:
+            except Exception:
                 logging.exception("Mind map generation error")
 
         vects = embedding(doc_id, [c["content_with_weight"] for c in cks])